Coalesce async touch move events until the ack back from render

content/common/input/web_input_event_traits.cc

Index: content/common/input/web_input_event_traits.cc
diff --git a/content/common/input/web_input_event_traits.cc b/content/common/input/web_input_event_traits.cc
index 6ca962b5720d9741d2b6bc4d4d251f7e9a86b9ec..f4b3207575d26ef0650171cb848c51e7ab44c8e2 100644
--- a/content/common/input/web_input_event_traits.cc
+++ b/content/common/input/web_input_event_traits.cc
@@ -478,8 +478,9 @@ bool WebInputEventTraits::IgnoresAckDisposition(const WebInputEvent& event) {
     case WebInputEvent::GesturePinchEnd:
     case WebInputEvent::TouchCancel:
       return true;
+    // For all touchmove events, we always need an ACK back from render, and
+    // for uncancelable touch move, we will also send a fake ACK.

[tdresser, 2015/03/26 15:25:29]

Hmmm, this is a bit confusing. (Sorry I didn't catch this earlier)

We do ignore the disposition of an uncancelable touchmove, but we still care
about when the ack is sent.

Based on the name of this method, I'd expect TouchMove to be in this list. Can
we put it back? 

[lanwei, 2015/03/27 04:39:42]

Done.

     case WebInputEvent::TouchStart:
-    case WebInputEvent::TouchMove:
     case WebInputEvent::TouchEnd:
       return !static_cast<const WebTouchEvent&>(event).cancelable;
     default: